This invention relates to new human monoclonal antibodies which react specifically with antigens associated with particular cancers and to hybridoma and transformed B-cell lines for their production derived from peripheral blood B-cells of actively immunized patients. This invention also relates to methods having general applicability to all solid cancers for preparing hybridomas and monoclonal antibodies and to diagnostic procedures and cancer therapy using these monoclonal antibodies.
Currently available treatments for cancer, particularly radiation therapy and chemotherapy, are based upon the rationale that cancer cells are relatively more sensitive to these treatments than normal cells. However, severe toxicity for normal tissues imposes major limitations to these therapies. In contrast, antibody molecules exhibit exquisite specificity for their antigens. Researchers have therefore sought to isolate antibodies specific for cancer cells as the "long-sought `magic bullet` for cancer therapy" (Science, 1982, 216: 283).
Antibodies are protein molecules normally synthesized by the B-cell lymphocytes produced by bone marrow and carried in the blood stream. For any antigen entering the body, i.e., any foreign molecule from a simple organic chemical to a complex protein, antibodies are produced which recognize and attach to that particular chemical structure. The unique chemical structure on the antigen to which a particular antibody can bind is referred to as an antigenic determinant or epitope. B-cell lymphocytes in the body, referred to as B-cells, lymphocytes, or leukocytes, exist as hundreds of millions of different genetically programmed cells, each producing an antibody specific for a different determinant. An antigen, which stimulates antibody production, can have several determinants on its surface. On encountering an antigen, a B-cell carrying on its surface an antibody specific for a determinant on that antigen will replicate. This clonal expansion results in many daughter cells which secrete that antibody into the blood stream.
Because of the specificity of antibodies in recognizing and binding to antigens, it was desired to produce antibodies in quantity which are specific for a single determinant, thus binding only to antigens or tissues having that particular determinant.
B-cells do not grow in a continuous culture unless they have been altered by hybridization with an "immortal" cell or by being transformed with either viral or tumor DNA. Kohler and Milstein (Nature, 1975, 256: 495) demonstrated that hybrid cells could be prepared by somatic cell fusion between lymphocytes and myeloma cells which grow in culture and produce an antibody specific for a single determinant. These hybrids are referred to as "hybridoma cells." Hybridoma cells are prepared by fusing lymphocytes, which have been activated to produce a particular antibody, with myeloma cells. When cultured, hybridomas produce antibodies specific for a single determinant on a particular antigen. Such antibodies are referred to as "monoclonal antibodies."
Monoclonal antibodies may also be produced by B-lymphocyte cell lines that have been spontaneously transformed, either prior to or subsequent to being placed in culture. These cells, in distinction to hybridoma cells, possess a normal human diploid number (46) of chromosomes. This invention permits the isolation of both hybridomas and transformed B-cell lines that produce monoclonal antibodies. For sake of simplicity, both cell types will be referred to as monoclonal antibody producing cells below.
Monoclonal antibodies are synthesized in pure form by a monoclonal antibody producing cell cultures uncontaminated by other immunoglobulins. With such a cell culture, it is possible to produce virtually unlimited quantities of an antibody that is specific for one determinant on a particular antigen.
It has been believed that if antibodies specific for particular cancer cells were available, they could be used in various methods of treatment and diagnosis. Such antibodies could inactivate or kill particular tumor cells merely by attaching to the cell at the determinant for which they are specific. Alternatively, these antibodies may bind to the surface of effector lymphocytes or macrophages, converting them into tumor antigen-specific killer cells.
Monoclonal antibodies can also increase the specificity of chemotherapeutic drugs, toxins and radioactive isotopes, thus increasing their efficacy while decreasing their toxicity. A monoclonal antibody can be conjugated with a toxin, radionuclide or chemotherapeutic drug; this conjugated antibody may be simplistically viewed as a guided missle with the antibody as the guidance system and the drug as the warhead. In addition, antibodies conjugated with radionuclides or metallic tracers can be used for proton emission (PET) and nuclear magnetic resonance (NMR) imaging for in vivo diagnosis and localization of metastases. The antibodies can also be used for detecting the presence of tumor antigens in blood, as a diagnostic and/or prognostic test for cancer. Also, monoclonal antibodies can be used to isolate the tumor antigens for potential use in a standardized vaccine.
The existence of antigens associated with animal tumors was documented in the last century, and the antigenic character of human cancers has been well established, primarily through recent studies with monoclonal antibodies. However, until the research which resulted in this invention, few cancer antigens have actually been characterized in molecular terms and only one group of antigenic determinants associated with human cancers, immunoglobulin idiotypes of B-cell tumors, has been described as being uniquely tumor-specific, i.e., occurring with a high frequency on tumor cells and not occurring to any significant degree on normal tissues (Oldham and Smalley, J. Biol. Response Modifiers, 1983; Stratte et al, J. Biol. Response Modifiers, Volume 1 1982).